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Biomedical subjects

W Voelker

Publications and source records attributed to W Voelker.

At least 73 records · Page 4Linked to original sources
PubMed1991

Intraoperative valvuloplasty in calcific aortic stenosis: a study comparing the mechanism of a novel expandable device with conventional balloon dilatation.

In selected patients with calcific aortic stenosis, balloon valvuloplasty is an intermediate alternative to surgery. The effect of balloon valvuloplasty to increase valve area, however, is limited and the restenosis rate is high during follow-up. To improve the results and reduce the complication rate, a new device for valvuloplasty of calcific aortic stenosis was developed. This system consists of three expandable prongs mounted on a freely movable catheter tip. To evaluate the efficacy of this new device, valvuloplasty was performed in 10 patients with severe aortic stenosis intraoperatively just prior to valve replacement. Comparison was made with the results of conventional balloon dilatation performed in an additional 20 patients during surgery. Using the new device, the relative orifice area increased from 10 +/- 3% before to 20 +/- 6% following intervention. However, in only one patient was a considerable increase of static valve area (greater than 15%) found. The results were comparable to the effect of conventional balloon dilatation, which led to an increase of orifice area from 12 +/- 7% to 24 +/- 10%. With both systems, the best results were achieved in patients with aortic stenosis and significant commissural fusion. In contrast, in bicuspid or tricuspid valves without fused commissures the effect of the intervention was limited. Because complete obstruction of the aortic valve does not occur during dilatation, this new device might be superior to conventional balloon dilatation. Preselection of patients according to the morphology of the valve seems mandatory to improve the success and reduce the complication rate of valvuloplasty in aortic stenosis.

Aged↗
PubMed1991

Effects of intracoronary nitroglycerin on lumen diameter during early follow-up angiography after coronary excimer laser atherectomy.

The incidence of coronary vasospasm during and following excimer laser atherectomy is considerable. The aim of this study was to investigate vasoconstriction of the target vessel during early follow-up angiography. In 50 patients an angiogram was performed 24 hours after intervention. Nineteen patients were treated with stand-alone laser atherectomy (group I), another 19 with laser and additional balloon angioplasty (group II) and 12 with balloon angioplasty alone (group III). Lumen diameter and percent stenosis before and after intracoronary application of 0.1 mg nitroglycerin were determined. The differences were compared between groups I, II and III, and for patients with (N = 14) and without (N = 24) vasospasm during laser atherectomy. There was a significant increase in lumen diameter, of 0.17 +/- 0.28 mm, after nitroglycerin in group I, of 0.18 +/- 0.29 mm in group II (P = 0.02) and of 0.03 +/- 0.21 mm in group III (ns). In patients with vasospasm during laser atherectomy the average increase in lumen diameter was 0.28 +/- 0.24 mm (P less than 0.01), and in patients without vasospasm 0.12 +/- 0.29 mm (P = 0.09). We conclude that one day after coronary excimer laser atherectomy intracoronary nitroglycerin significantly affects lumen diameter at the site of previous stenosis, an effect undetectable after balloon angioplasty. Thus, vasoconstriction after excimer laser ablation seems to be a common phenomenon and is prolonged in patients with vasospasm during the previous intervention.

Adult↗
PubMed1991

[Perforation of the vascular wall after coronary excimer laser angioplasty].

A 56-year-old patient with recurrent episodes of angina pectoris at rest was admitted for left-heart catheterization. The coronary angiogram revealed two-vessel disease with a subtotal stenosis in the circumflex artery and a long 90% stenosis in the proximal part of the left anterior descending artery. On the basis of symptoms and coronary morphology laser angioplasty was performed. After a total of 99 s of energy delivery extravasation of dye occurred at the site of ablation. Due to acute vessel occlusion subsequent PTCA was performed, resulting in a satisfactory angiographic result. Extravasation of dye was terminated after PTCA and was absent at short-term follow-up angiography. No signs of pericardial effusion were detectable by two-dimensional and M-mode echocardiography. A control angiogram disclosed the identical result the day after the acute intervention, and the patient could be discharged with a normal exercise test 1 week later.

Angina Pectoris↗
PubMed1990

[Myocardial effects of the calcium antagonists nifedipine, nisoldipine and isradipine in coronary heart disease].

Cardiac and peripheral effects of three calcium antagonists of the dihydropyridine group were compared in three groups of ten men each with coronary heart disease (mean age 56 +/- 6 years). Dosages (by 30 minutes intravenous infusions) were: 2 mg nifedipine in group I, 0.5 mg nisoldipine in group II and 0.5 mg isradipine in group III. In this dosage peripheral effects--decrease of peripheral vascular resistance and mean aortic pressure--did not differ significantly between them. As a consequence of different negative chronotropic properties the extent of the observed reflex tachycardia was different: there was no significant heart rate increase after isradipine, an increase by 9.8% (P less than or equal to 0.001) after nifedipine and by 20.4% (P less than or equal to 0.001) after nisoldipine. Left-ventricular pressure-rise velocity as a parameter of myocardial contractility rose by 15.3% in group II (P less than or equal to 0.001) and by 13.5% in group III (p less than or equal to 0.001), but not in group I. These data show, that peripheral equipotent dosages of the three calcium antagonists can have different myocardial effects.

Blood Pressure↗
PubMed1990

Doppler measurement of cardiac output across prosthetic mitral valves.

In 46 patients with a normal functioning mitral valve prosthesis (15 St. Jude, 19 Medtronic Hall, 12 Hancock) cardiac output was measured by pulsed Doppler echocardiography across the valve prosthesis. Simultaneously cardiac output was determined by thermodilution or pulsed Doppler echocardiography in the left ventricular outflow tract (2.8 l/min-9.5 l/min). The prosthetic valve area was calculated using the pressure half-time method. Cardiac output was calculated by multiplying time-velocity integrals with the mitral valve area. Cardiac output measurements across the mitral prosthesis correlated significantly with thermodilution (r = 0.96, SEE = 0.400 l/min) and pulsed Doppler echocardiography flow measurements in the left ventricular outflow tract (r = 0.82, SEE = 0.679 l/min). The mean percent error of the Doppler transmitral flow measurement was 10.8%. Doppler transmitral flow underestimated cardiac output valves of more than 6.5 l/min in 6 of 7 patients. Cardiac output measurements across Hancock (SEE = 0.473 l/min) and St. Jude prostheses (SEE = 0.538 l/min) were more accurate than across Medtronic Hall prostheses (SEE = 0.847 l/min). Cardiac output can be calculated by pulsed Doppler echocardiography across normal functioning mitral prostheses. Due to the different flow dynamics the accuracy of cardiac output measurement depends on the prosthetic valve type. Reliable measurements of cardiac output can be performed across Hancock and St. Jude prostheses only. This method is limited in volume flow measurements across Medtronic Hall prostheses.

Adult↗
PubMed1990

[Validation of a Doppler catheter for intravascular flow measurement in vivo. A comparison with simultaneous electromagnetic flow measurement].

A new 3-French Doppler catheter has recently been developed for direct measurement of blood flow velocity within the vessel. In in-vitro studies Doppler and real flow measurements correlated strongly. To validate this method in-vivo, phasic flow measurements in the aorta ascendens of 11 narcotized Wistar rats using Doppler and an external electromagnetic flowmeters were performed. The individual stroke volume was varied over a wide range. High intraindividual correlations were found (r = 0.92-0.99). However, a considerable variation of the slope a of the regression lines was noted (a = 0.42-1.47). Thus, qualitative registration of phasic flow is possible and relative changes of flow can be determined with sufficient accuracy through intravascular Doppler measurements. Probably due to interindividual differences of the catheter position within the vessel, however, measurements of absolute flow volumes are unreliable in this setting.

Animals↗
PubMed1990

Myocardial and coronary effects of captopril during pacing-induced ischaemia in patients with coronary artery disease.

It has been speculated that ACE inhibitors may have beneficial effects in patients with coronary artery disease not only by their vasodilator properties but also by an effect on an assumed local renin-angiotensin system in atherosclerotic coronary arteries. Thus, the aim of the present study was to evaluate the effect of a single intravenous infusion of captopril on haemodynamics and coronary diameter at rest and during myocardial ischaemia induced by rapid atrial pacing. The study was performed in 12 patients with coronary artery disease and exertional angina pectoris despite medical therapy. Central haemodynamics (PAO, PAP) and left ventricular end-diastolic pressure were measured. Biplane cineventriculography and coronary arteriography were performed during control pacing (10% above the normal heart rate) before and after 15 min of captopril infusion, as well as during angina pectoris induced by rapid atrial pacing before and after captopril (six patients 0.15 mg kg-1, six patients 0.3 mg kg-1). Mean aortic pressure was not significantly decreased by either 0.15 mg kg-1 or 0.3 mg kg-1, whereas mean pulmonary pressure was significantly reduced by captopril by 28% at rest and 34% during rapid atrial pacing. Neither the endsystolic volume index nor left ventricular ejection fraction was significantly affected by captopril. Left ventricular end-diastolic volume index was reduced by 9% at rest and 7% during pacing-induced angina. Left ventricular end-diastolic pressure decreased from 11 +/- 9 mmHg to 4.8 +/- 4.1 mmHg at rest after captopril, and from 10 +/- 11 mmHg to 5.1 +/- 5.0 mmHg during pacing-induced angina after captopril.(ABSTRACT TRUNCATED AT 250 WORDS)

Angina Pectoris↗
PubMed1990

Percutaneous coronary excimer laser angioplasty in patients with stable and unstable angina pectoris. Acute results and incidence of restenosis during 6-month follow-up.

A clinical study was conducted to evaluate the efficacy and safety of percutaneous coronary excimer laser angioplasty in 60 patients with coronary artery disease. Forty-nine patients had stable exertional angina, and 11 patients had unstable angina despite medical therapy. A novel 1.4-mm diameter catheter with 20 quartz fibers of 100-microns diameter each arranged concentrically around a central lumen suitable for a 0.014-in. flexible guide wire was coupled to an excimer laser. A commercial excimer laser emitting energy at a wavelength of 308 nm with a pulse duration of 60 nsec was used. The laser was operated at 20 Hz. Mean energy transmission was 30 +/- 5 mJ/mm2. In five of the 60 patients, laser angioplasty was not attempted. In 23 patients with laser ablation alone, percent stenosis decreased from 76 +/- 14% before to 27 +/- 17% after ablation and was 34 +/- 15% at the early follow-up angiogram. In 32 patients, additional balloon angioplasty was performed because of vessel closure after laser ablation in 11 and an insufficient qualitative result in 21 patients. Of the 11 patients with unstable angina, one patient died due to vessel closure 3 hours after intervention, and two patients developed a myocardial infarction. In 22 of 47 patients with late follow-up angiography, restenosis within the 6-month follow-up period occurred. Rate of restenosis was higher in patients treated with laser ablation and balloon angioplasty (16 of 28) than in patients treated with laser ablation alone (six of 19). These results suggest that coronary excimer laser angioplasty for ablation of obstructive lesions is feasible and safe in patients with stable angina. However, development of new catheter systems is necessary for an improved success rate.

Adult↗
PubMed1990

[Occluding spasm of the total left coronary artery during coronary angiography].

Catheter-induced coronary artery spasms are rare during diagnostic coronary angiography, and they occur more often after PTCA because of local vessel wall injury. These spasms are rapidly reversible after administration of nitroglycerine and are normally no cause of serious complications. We report about a catheter-induced occlusive spasm of the entire left anterior descending and circumflex coronary artery in a 56-year-old patient with coronary double-vessel disease, 70% restenosis of the LAD, and a history of two coronary angiographic procedures and one PTCA without any complication. The spasm occurred immediately after the intubation of the left main stem with a 9F PTCA guiding catheter before the coronary guide wire or balloon was advanced into the LAD. Cardiac resuscitation was necessary due to acute left heart failure. The spasm was spontaneously reversible, but reproducible. Therefore, life-threatening coronary artery spasm can occur during coronary angiography or PTCA, but the tendency of spontaneous spasm relief seems to be high.

Angioplasty, Balloon, Coronary↗
PubMed1990

[Percutaneous coronary excimer laser angioplasty].

Available preliminary clinical studies have shown that ablation of atherosclerotic plaques can be achieved by means of pulsed excimer laser coronary angioplasty via flexible energy transmission systems. The goal of current studies using improved catheter technology is to enhance the acute success rate since, based on initial studies, it can be assumed that only about 40 to 45% of the patients can be successfully treated. The on-going investigations were carried out primarily with three different excimer laser systems which employ a wavelength of 308 nm but differing pulse widths and transmission systems. In the first American multicenter study by Litvack and Margolis a catheter system was used with a pulse width of 180 to 220 ns. The fibers have a shaft diameter of 100 microns with a conically-thickened distal end measuring 200 microns, the ablative area encompasses 35 to 45% of the total catheter tip surface. The excimer laser used in the second American multicenter study by Sanborn and Isner has a pulse width of 120 ns. This catheter is relatively unflexible due to the 200 microns fiber diameter. The ablative catheter tip area is 25 to 30%. In Tübingen a system was used with a pulse width of 60 ns. The energy is transmitted through fibers with a diameter of 100 microns. The effective ablative area in the first series of patients was about 15%, in the second series about 25 to 30%. At present, the energy density of all three systems is comparable with at least 25 to 35 mJ/mm2. Since there is currently no means for accurate assessment, the question of whether a shorter pulse width of comparable energy density is more effective than the longer pulse width, remains an open issue. The flexibility of the systems used by Margolis and in Tübingen enable ablation not only of proximal, but also arteriosclerotic plaques located in the middle-third of vessels. The flexibility and steerability, however, are inferior to balloon catheter systems. In the study carried out by Litvack and Margolis, in which more than 600 patients have been treated, and the results from 514 patients reported, there was no patient selection in the first series. The study by Sanborn and Isner included 88 patients. Due to the relatively unflexible catheter system, only those patients were treated who had proximal stenosis of the left anterior descending or right coronary artery or marginal branches of the circumflex artery without marked tortuosity.(ABSTRACT TRUNCATED AT 400 WORDS)

Angioplasty, Balloon, Coronary↗
PubMed1990

[Effect of acute short-term ischemia during PTCA on the function of the right ventricle].

To determine whether a transient ischemia of the right ventricle leads to right ventricular impairment and whether RV function can also be influenced by septal ischemia caused by an occlusion of the left anterior descending coronary artery (LAD), RV function before and at the end of 60 s of ischemia during PTCA was assessed in 15 patients with single-vessel disease of either the right coronary artery (RCA, n = 10) or the LAD (n = 5). The RV-enddiastolic pressure and the pulmonary capillary wedge pressure (PCW) were recorded continuously. The RV ejection fraction was determined from ventriculograms performed before and during coronary occlusion. An increase of RVEDP from 3.7 +/- 1.2 to 8.3 +/- 1.8 mm Hg (p less than or equal to 0.001) and a decrease of the RV-ejection fraction from 52 +/- 3 to 33 +/- 8% (p less than or equal to 0.001) occurred during RCA occlusion with a predominant ischemia of the RV free wall only, and not during LAD occlusion with left ventricular and septal ischemia. The extent of the RV dysfunction was independent of an additional increase of RV afterload (PCW increase). Comparable to ischemic effects on left ventricular function, an acute right ventricular myocardial ischemia results in a severe RV contractile failure.

Angioplasty, Balloon, Coronary↗
PubMed1990

Continuous arterial positron monitor for quantitation in PET imaging.

Quantitative measures of physiologic function with PET require continuous monitoring of arterial positron isotope concentration. A device has been developed that automates this process. This device has advantages over manual sampling techniques with syringes since fewer personnel are required, measurements are less error prone, and more continuous measures of arterial positron concentration are available. A constant flow infusion/withdrawal pump withdraws blood from the radial artery through a catheter connected to 0.5 mm inner diameter teflon tubing. This tubing is wrapped around a 50 mm thick by 50 mm diameter NaI(T1) crystal that is interfaced to a photomultiplier tube (PMT) and encased in a cylindrical lead shield. This crystal detects 511 Kev photons that result from positron annihilation. The device sensitivity is greater than 240 (cts/sec)/(microCi/ml) corresponding to a peak activity of approximately 10,000 cts/sec for a 50 mCi bolus injection in an adult. The system dynamic response has been measured and the true arterial input function is recovered by deconvolution. The system has been used clinically for more than 400 human PET studies and has been a reliable continuous monitor of arterial positron concentration.

Arteries↗
PubMed1990

[Percutaneous coronary Excimer laser angioplasty in patients with coronary heart disease].

To verify the efficacy and safety of percutaneous coronary excimer laser angioplasty in patients with coronary artery disease a prospective study was conducted in 60 patients. The application of laser light was possible in 55 of the 60 patients. A novel 1.4-mm diameter catheter with 20 quartz fibers of 100-microns diameter, each arranged concentrically around a central lumen suitable for an 0.014-inch flexible guide wire was used. The light source was a commercial excimer laser emitting energy at a wavelength of 308 nm, with a pulse duration of 60 ns. The laser was operated at 20 Hz; mean energy transmission was 30 +/- 5 mJ/mm2. In 23 of the 55 patients treated with excimer laser energy the qualitative angiographic results were sufficient. In 32 patients additional balloon angioplasty was necessary, either because of an insufficient result or due to vessel closure after laser ablation. In 47 of the 55 patients control angiography was performed within the 6-month follow-up period. Rate of restenosis was higher in patients treated with laser ablation and subsequent balloon angioplasty (16 of 28) than in patients treated with laser ablation alone (6 of 19). Results of the 6-month observation period suggest that 1) coronary excimer laser angioplasty in combination with subsequent balloon angioplasty results in a considerable increase of the restenosis rate; 2) the exclusive use of laser ablation also results in a restenosis rate comparable to balloon angioplasty alone; and 3) the impact of this new method using improved application systems and higher energy transmission has to be determined in further studies.

Angina Pectoris↗
PubMed1989

Initial angiographic results in ablation of atherosclerotic plaque by percutaneous coronary excimer laser angioplasty without subsequent balloon dilatation.

Percutaneous transluminal coronary excimer laser angioplasty was performed in 15 patients using a 1.3-mm diameter laser catheter. The catheter consists of 20 concentric quartz fibers of 100 microns diameter each located around a central lumen suitable for a 0.014-inch flexible guidewire. The catheter was coupled to an excimer laser delivering energy at a wavelength of 308 nm and at a pulsewidth of 60 ns. Quantitative analysis of the angiograms documented a decrease from 77 +/- 15% diameter stenosis before intervention to 40 +/- 22% after the first irradiation cycle and to 21 +/- 17% after termination of laser ablation. The minimal lumen diameter increased from 0.4 +/- 0.2 to 1.3 +/- 0.4 and to 1.6 +/- 0.4 mm, respectively. Vessel reocclusion was seen in 2 patients at 24-hour control angiography. No procedure-related major complications such as vessel perforation occurred. In 8 patients, however, intraluminal lucencies were seen, which were persistently visualized 24 hours after intervention in 6 patients. Despite pretreatment with intracoronary nitroglycerin, coronary spasm occurred in 8 patients and was reversible after additional sublingual vasodilator therapy. The results of this pilot study suggest that percutaneous coronary excimer laser angioplasty is feasible and effective for ablation of coronary lesions in selected patients and can be performed without subsequent conventional balloon angioplasty. The clinical impact of this new interventional technique, however, remains to be assessed.

Angiography↗
PubMed1989

Percutaneous coronary excimer laser angioplasty: initial clinical results.

A novel 1.3 mm diameter laser catheter, consisting of 20 concentric 100 microns quartz fibres around a central lumen for a 0.35 mm flexible guide wire, was used to ablate atherosclerotic tissue in thirty patients with coronary artery disease. The laser catheter was coupled to an excimer laser delivering energy at a wavelength of 308 nm and a pulsewidth of 60 ns. The primary success rate was 90% (27 of 30 lesions). The mean (SD) percentage stenosis fell from 85 (15)% to 41 (19)% after laser ablation. In ten patients the lumen diameter after laser angioplasty was considered sufficient, but subsequent balloon angioplasty was carried out for the other twenty patients. Failure to pass the lesion was caused by vessel kinking in two patients and a total occlusion in one patient. No complications directly attributable to laser ablation, such as vessel wall perforation, occurred; one dissection occurred but had no clinical sequelae. There was one early reocclusion and death in a patient with triple vessel disease and unstable angina, probably as a result of plaque rupture after balloon angioplasty. These results are encouraging and justify further clinical investigations.

Angioplasty, Balloon↗
PubMed1989

[Doppler echocardiography quantification of the regurgitant blood volume in patients with mitral valve insufficiency].

The purpose of this study was to assess the accuracy and clinical utility of pulsed Doppler echocardiography in determining the regurgitant fraction in patients with pure mitral regurgitation. In 30 unselected consecutive patients with mitral regurgitation and in 20 patients without valvular heart disease pulsed Doppler echocardiography was performed to measure blood flow at the mitral and aortic valve. The regurgitant blood volume was calculated as the difference of the stroke volumes measured at the mitral and aortic valve. The regurgitant fraction was computed as regurgitant blood volume/mitral flow. By cardiac catheterization regurgitant blood volume and regurgitant fraction were obtained from the left ventricular angiographic stroke volume and the stroke volume measured by thermodilution. Five patients were excluded because of technically poor left ventricular angiograms. In 4 patients with mitral regurgitation measurement of the regurgitant blood volume and regurgitant fraction was impossible by Doppler because of poor ultrasound signal quality. In 21 patients with mitral regurgitation the correlations between the invasive and the Doppler measurements were significant (regurgitant blood volume: r = 0.89, SEE = 20.9 ml; regurgitant fraction: r = 0.91, SEE = 7.1%). However, the mean percent error of the regurgitant fraction measurement (12.0 +/- 11.6%) was smaller than of the regurgitant blood volume measurement (24.9 +/- 17.0%). In the control group the regurgitant blood volume ranged between -25.1 ml and 11.6 ml and the regurgitant fraction between -17.7% and 12.4%. Thus, pulsed Doppler echocardiography is clinically useful in determination of the regurgitant fraction in 84% of unselected adult patients with pure mitral regurgitation. The Doppler method is limited in the diagnosis and quantification of mild regurgitation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

[Percutaneous transluminal excimer laser coronary angioplasty].

Percutaneous transluminal laser coronary angioplasty (PTLCA) was undertaken in five patients (four men and one woman, aged 44-72 years) with coronary artery stenosis. The vessel diameter was increased in all patients after PTLCA; complete ablation of the atheromatous plaque succeeded in three. In the other two the catheter could not be advanced across the entire stenotic region. After PTLCA the stenoses were 40-50% of normal lumen. Balloon dilatation was additionally done in all five patients. In three this caused dissection of the vessel wall distal to the stenosis and possible intracoronary thrombus formation: this would suggest that balloon dilatation after laser angioplasty is not recommendable. PTLCA widens the spectrum of invasive methods for treating coronary artery stenosis.

Adult↗